Expert Critique

Incorporating exercise for patients with diabetes (type 1 and type 2) is critical for maintaining good cardiovascular, skeletal, and mental health. However, it must be undertaken with careful planning.

The author provides a wonderful personalized review of his approach to exercise and insulin adjustments. To start, there is a different mindset even before a person starts to sweat. Being aware of blood sugar levels before exercise is the first step; if the blood sugar is already high (>200), there is an increased risk of dehydration and a small correction dose of insulin may be useful. If the blood sugar is on the low end of normal <100, eating a snack before the workout will reduce risk of hypoglycemia.

The type of exercise – aerobic or anaerobic – plays a key role in the blood sugar trend during exercise. Aerobic exercise of moderate intensity (such as jogging, swimming or cycling) tends to cause a slow decrease in blood glucose in those with diabetes mellitus type 1 (DM1) as sugar is taken up by active muscle tissue via GLUT4 receptors; exogenous insulin given by injection or a pump will fail to decrease, thus limiting hepatic gluconeogenesis and blood sugar can drop. On the other hand, anaerobic exercise in DM1 patients may actually lead to a rise in blood sugar due to release of catecholamines (adrenaline-like hormones); failure of insulin levels to rise in response to this surge of stress hormones thus results in a rise in blood sugar. One approach that may work is completing the anaerobic activities, such as weight-lifting or bursts of high intensity exercise, at the beginning of the workout, then followed by aerobic/cardio training. This may blunt the trend towards hypoglycemia for these patients.

After exercise, the author points out the important effect of improved insulin sensitivity, which may lead to delayed-onset hypoglycemia. Thus, bolusing for foods after exercise also needs to be adjusted, such that a unit of insulin that would usually cover 10 grams of carbohydrate may cover 15 or 20 grams.

One final consideration for patients who have difficulty maintaining stable blood sugar during or after exercise would be use of an insulin pump and/or continuous glucose monitor (CGM). Insulin pumps allow for patients to use a temporary bolus feature before, during and after exercise to reduce their basal rates depending on the duration and intensity of exercise anticipated. This may not be ideal for every patient, but should be considered by physicians who treat those with diabetes.

Full Critique

I previously discussed the many physiological responses exercise has on the body specifically for those with type 1 diabetes. Routine exercise increases the body's insulin sensitivity allowing carbohydrates to be more readily processed. People who exercise regularly will also see benefits in lower blood pressure, better weight control, stronger bones, and increased energy. But, there are many pitfalls to exercise such as increased risk of hypoglycemia, thus it is very important for clinicians to advise people with diabetes to become educated and eventually develop their own personalized approach. In fact, professional football player, Jay Cutler is living with type 1 diabetes and is a testament that active competition can certainly be accomplished.

Pre-workout

What type of exercise?

Aerobic exercise such as running, competitive sports, and class workouts cause persistent elevations in your heart rate and consequently glucose is burned fast. It is excellent for your overall cardiovascular fitness, but can put you at an acute risk for hypoglycemia both during and following a workout.

Anaerobic activity such as strength training can initially cause an increase in blood glucose levels because of the release of epinephrine and norepinephrine, causing the liver to release more glucose into the blood. It is important not to counteract this increase in blood glucose with insulin as it is a normal response allowing muscles to rebuild. A few hours after a workout these counterregulatory hormones decrease and hypoglycemia can occur.

This journal article, which examines in depth the effects of different forms of exercise and diabetes management, can help your patients develop an exercise plan.

What time of day is best to exercise?

I have always noted that my blood sugar tends to run higher in the morning, mostly because of a cortisol spike. Increased levels of cortisol, referred to as the "stress hormone," gets us ready to take on our day, but can also increase blood sugar levels. Thus, when I exercise in the morning, I know that I will require less insulin for every 15-20g of carbohydrate.

I avoid exercising shortly before sleep because I want to avoid nocturnal hypoglycemia.

What should my pre-exercise blood glucose level be?

Unfortunately, there is no doctor-recommended exact number, but there are a few methods I have learned through trial and error.

I aim to keep my blood glucose levels between 120 and 180 prior to exercise; closer to 120 for anaerobic exercise and 180 for aerobic exercise. Some individuals may recommend a starting level as low as 80, but I believe it is safer to be mildly hyperglycemic and avoid hypoglycemia. Plus, nothing kills a workout faster then suddenly becoming shaky, sweaty and just plain sluggish.

I personally never exercise on an empty stomach because I have found this almost always leads to low blood sugar.

What types of foods should I eat prior to a work out?

Consistency is key. I only eat foods that I have tried before because I know how my blood sugar will respond. I usually eat the same granola bar prior to a workout. I may also adjust this based on how much I have already eaten that day, how long I plan to exercise, and the intensity of the workout.

University of California, San Francisco provides guidance on how many grams of carbohydrates should be consumed prior to various activities. I find this an excellent resource.

For longer workouts, I include more protein and fat, such as peanut butter, in my pre-exercise snack. Protein and fat slow down your body's rate of absorption thereby helping prevent low blood sugar.

Individuals with type 2 diabetes may find this resource from the Cleveland Clinic helpful as it outlines specific foods to eat prior to a workout .

During a workout

What should I do if my blood glucose is low?

Many T1Ds follow the "15-15 rule" which is to consume a food with 15 grams of carbohydrates and recheck your blood sugar in 15 minutes. I usually carry a granola bar with me to the gym in case of this scenario.

It is best to have simple sugars, which will quickly raise your glucose level, such as 4 ounces of fruit juice or 3 glucose tablets. Do not eat a snack high in fat or protein as this will delay normalization of your blood sugar .

What about use of a continuous glucose monitor (CGM) during exercise?

Some type 1 diabetes patients relate that CGM has made an enormous impact on managing their blood sugar both in general and during exercise. However, it is important to be thoroughly educated on how to best utilize this new tool and it should not completely replace the use of a glucometer.

There are conflicting data on the long-term benefits of CGMs such as prevention of long-term complications and mortality improvement. The primary indication is for patients who have poor control of their blood sugar, specifically frequent episodes of hypoglycemia.

Blood glucose can continue to decrease several hours after a workout. I usually eat within 30 minutes and choose foods high in protein and fat to prevent hypoglycemia. Also, certain foods such as an apple and peanut butter may normally require 2 units of insulin, now only require 1 unit due to increased insulin sensitivity.

My hope is that I was able to provide a deeper understanding of the relationship of exercise and its effects on insulin and blood glucose. Each individual develops his or her own tailored approach and I enjoy sharing my own in hope that it will help others achieve better control.